I. Field of the Invention
The present invention relates generally to surgical fixation and, more particularly, to systems and methods for treating spinal deformities.
II. Discussion of the Prior Art
The human spine exhibits some degree of curvature at different levels to facilitate normal physiologic function. Correction of the spine may be required when the curvature of the spine deviates substantially from normal. The misalignment usually manifests itself in an asymmetry of the vertebral bodies, such that, over a sequence of vertebrae, the spine twists and/or bends to one side. This lateral deviation of the spine is commonly termed scoliosis.
Spinal deformity occurs when a patient has abnormal frontal or sagittal plane alignment. At the same time, the cervical and lumbar spine exhibit lordosis, while the thoracic spine has kyphosis. Thus, when performing spinal fusion, surgeons may be required to preserve or restore both front plane and sagittal alignment while taking lordosis and kyphosis into account. Scoliosis can develop later in life, as joints in the spine degenerate and create a bend in the back which may require surgery.
Surgery has traditionally involved procedures such as the Harrington, Dwyer and Zielke, and Luque procedures which rely on implanted rods, laminar/pedicle hooks, and screws to maintain the correction until stabilized by fusion of vertebrae. According to these surgical techniques, treating scoliosis includes the implantation of a plurality of hooks and/or screws into the spinal bones, connecting rods to these elements, physically bracing the bones into the desired positions, and permitting the bones to fuse across the entire assembly. This immobilization often requires anterior plates, rods and screws and posterior rods, hooks and/or screws. Alternatively, spacer elements are positioned between the sequential bones, which spacers are often designed to permit fusion of the bone into the matrix of the spacer from either end, hastening the necessary rigidity of the developing bone structure.
The Harrington instrumentation system has been used successfully for some time, but because the distraction rod is fixed to the spine in only two places, failure at either end causes the entire system to fail. Another deficiency with existing mechanisms and approaches is that the single rod used to correct the defects must be contoured to fit various attachment sites. In patients having compound spinal deformity, this may be extremely difficult. A further problem is that the contoured rod frequently limits further correction of certain types of deformities. That is, once the rod is in position, further correction of the deformity is difficult, since existing systems tend to limit incremental alignment procedures.
The present invention is directed at overcoming, or at least improving upon, the disadvantages of the prior art.